The present invention relates to the field of wafers inspection, more specifically the present invention relates to a method and a system for inspecting the existence of voids in a bump and calculating the voids' volume.
A “bump” is a half sphere shaped salient, made of solderable material, located on the face of a microelectronic chip. The bump exists in some chips and substitutes as leads by means of which the component is connected to the printed circuit when the bumps are soldered to the board. The bump shape is a half ball alike and a chip can contain a large number of bumps. During the last few years the electronics industry moved from SnPb solders to Lead-free solders. Today the high lead SnPb bumps are exempted from the WEEE and RoHS directives. In the new wafers technologies a use of SnAg can be found instead of SnPB.
The typical bumps' dimensions are 50-60 μm in diameter and 20-30 μm in height. The skullcap is placed on a 50-60 μm diameter pillar of Copper with a height of approximately 50 μm. The whole structure is placed on a Silicon base with a top layer of passivation made of polymer.
During the wafer's production voids can be created in the soldering layer of the bump and in case that the volume of the voids passes a threshold the quality of the product is damaged. Usually, a threshold of 0.01% of volume is used in the wafer's quality inspection.
The present invention uses two well stable technologies to recognize void or voids in a bump and estimates the total volume of the voids inside the bump.
There are several technologies for calculating the volume of an object using 3D imaging process, one of these technologies is the first that is used in the present invention.
The second technology known as ED-XRF (Energy-Dispersive-X-ray-Fluorescence analysis) this technology is a well-established and stable technology used for years in the industry. In the last two years there was a great advance in this technology with the adoption of SD Detectors that enable much better resolution and count rate. This gives the ability to go down to lower levels of detection limits in much less time. This technology is a spectroscopy method belongs to the high energy spectroscopy process. The technology utilizes an emission of the characteristic lines. While an atom is hit by X-ray a characteristic energy is emitted from the atom and this energy is analyzed into the materials spectra of qualification and quantification. In a provided diagram, each of the bump's soldering material is presented as a column, the magnitude of the column represent the material volume.
X-ray optics can be used to enhance ED=XRF instrumentation. For conventional XRF instrumentation, typical focal spot sizes at the sample surface range in diameter from several hundred micrometers up to several millimeters. Polycapillary focusing optics collects X-rays from the divergent X-ray source and direct them to a small focused beam at the sample surface with diameters as small as tens of micrometers. The resulting increased intensity delivered to the sample in a small focal spot allows for enhanced spatial resolution for small feature analysis and enhanced performance for measurement of trace elements for Micro EDXRF applications.
The present invention combines these technologies and provides a method and a system for inspecting bumps.